The present invention relates to inkjet printheads. In particular, it relates to an arrangement of a bubble chamber and heater element in a printhead having a substantial offset from an orifice or nozzle of a nozzle plate.
The art of inkjet printing is relatively well known. In general, an image is produced by emitting ink drops from a printhead at precise moments such that they impact a print medium at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and to emit ink drops at times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
A conventional thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a barrier layer, a nozzle or orifice plate attached or formed with the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heater elements fabricated by deposition, masking and etching techniques on a substrate such as silicon.
To print or emit a single drop of ink, an individual heater is uniquely addressed with a predetermined amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local bubble chamber (between the heater and nozzle plate) and to be ejected through and projected by the nozzle plate towards the print medium.
With reference to FIGS. 1a and 1b, a typical geometry of a heater element 10 and a bubble chamber 12 relative to an orifice 14 in a nozzle plate 15 includes a substantially centered and symmetrical relationship. In particular, a plumb line 28 originating from an orifice center 30 has no lateral offset from a heater center 32. In addition, the orifice center exists substantially equidistant from each corner of the bubble chamber. As a result, stagnant regions 22 of the bubble chamber 12 serve to trap air bubbles in ink 16 that flows into the bubble chamber (through ink channel 20 and ink via 18) during use. Over time, trapped bubbles accumulate and grow large enough to prevent heat transfer from the heater element to the ink which eventually stops operation.
Accordingly, a need exists to prevent air bubble formation and accumulation in inkjet printheads.
The above-mentioned and other problems become solved by applying the principles and teachings associated with the hereinafter described printhead having a bubble chamber and heater element offset relative to a nozzle or orifice in a nozzle plate.
In one embodiment, the invention teaches an inkjet printhead with a substantially rectangular heater element. By dividing a length dimension by a width dimension, the heater element has an aspect ratio of more than about 2.0. More preferably, it has an aspect ratio of more than about 2.5, 4.0 or 5.0 or greater. A bubble chamber substantially surrounds the heater element with a plurality of walls that reside substantially equidistant from a periphery of the heater element. A nozzle plate covers the bubble chamber and has an orifice axially extending through a thickness thereof. A center of the orifice originates a plumb line such that an offset distance exists from a center of the heater element in a range from about 6 to about 10 microns, for example. An ink flow channel through one of the bubble chamber walls has a primary direction of ink flow substantially paralleling a length dimension of the heater element. The bubble chamber and ink flow channel may exist in the nozzle plate, in a barrier layer or in a plurality of film layers that define a heater chip. Inkjet printheads and inkjet printers for housing the printheads are also disclosed.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in the description which follows, and in part will become apparent to those of ordinary skill in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.